The present invention is directed to cable television systems wherein video signals are sent from a headend to individual subscriber terminals. As is well-known in the art, various levels of service are available to the subscriber terminals. Subscribers may choose from a wide variety of programs offered by a cable television system. Since a cable television system may provide many different programs, it is important to know which programs each individual subscriber terminal is authorized to receive. Additionally, it is necessary to send other information from the headend to a subscriber terminal for various other reasons, as is well known in the art.
One type of system for accomplishing these goals is a system using in-band data transmissions. Known in-band systems send authorization information and other information from the headend to the subscriber terminals over the same channel that is used to transmit video information. Such information may be sent on an addressable basis. One problem encountered with in-band systems is that in order for a subscriber terminal to receive information from a headend or other source, the video channel to which it is tuned must contain the data. Therefore, if information is sent out from a headend to all the subscriber terminals, only those terminals that are tuned to the appropriate frequency or channel will receive that information at that time. That gives rise to the need for providing refresh data, i.e., it is necessary to repetitively send out these data messages to ensure that all subscriber terminals will receive them.